Carburizer



March l7, 1939.

H. RODMAN CARBURIZER Filed May l, y1936 as ATTORNEY;

Patented Mar. "K7, 19359 omonima Hugh of Pennsylvania Rodman, Verona, Pa., Ghemical 'Companm Verona, Pa.,

assigner to Rodman a corporation Application May ll, 1936, ySerial F1o-77,329

Thisqnventio'n relates to carburizing by the dry pack method. l

It is among vide carburlzing compounds which are of simple composition, possess satisfactorily high carburizingq efficiency, are cheap, may be made by standard procedures and in any of the commercially desirable ph'ysical forms, and which minimize disadvantageous characteristics of manyprior art carburizing. compounds.

A further object is to provide carburizing compounds whlch exhibit carburizing activity at the usu'al carburizingtemperatures and which in addition possess unusually well-sustained activity in repeated use and require therefore the addition vof minimal amounts of fresh material.

Yet another object is to provide carburizing compounds embodying \the foregoing advantageous characteristics and which not only. are sim- 'jpler in composition and cheaper than the carburizing compounds used commercially, but also are of at Ileast equal, or comparable, carburizing Still another object is toiprovide carburizing compounds in which highand commercially acceptable carburizing activity ls attained predominantly or exclusively by the use of lime and certain metal oxides referred to hereinafter, and in which the use of barium carbonate and other relativelyl expensive energizers, or of a plurality of energizerais unnecessary. f Further objects are to provide carburizing compounds embcdying the foregoing desirable'features and characterizedby other advantageous features, singly or in combination, such asy pro-` duction of smooth-and evenly carburized surfaces, elimination of offensive and poisonous dust, and in the use of which attack upon thecarburizing containers is repressed or eliminated.

The invention will be described in connection with -the accompanying drawing, in which Fig. l is a graph showing the relative energizing powers of the commonly used alkali and alkalineearth metal energizers as a` function of their molecular weights; Fig. 2 agraph showing how the carburizing activity due to various energizers varies with the amount of energizerused in a carburizing compound; and Fig. 3 a graph illustratlve of the present invention.

Carbon itself, at least in any of its 4.common forms, possesses very low carburizing ability, and consequently the so-called energizers are mixeclA with carbon to provide'a mixture which will cause Ycarburization at a commercially acceptable rate.

The energizers commonly us'ed, i. e., carbonthe objects of the invention to prol ates or oxides of barium, sodium, and calcium,

burizing power of carbon. v

Lime, whether in the form of calcium carbon- .ate or calcium oxide, has been considered to be a very inemcienn energizer. In fact, used'alone it possesses much less energizing power than either barium carbonate or sodium carbonate and as far' as `I amaware, it has not been possible heretofore to make a carburizing compound which will satisfy modern requirements by the use of lime as thesole energizer. It is ordinarily used in minor amount in carburizers, however,y not to are not equally effective in increasing the car- A materially add to the energizing effect produced by barium carbonate, or other powerful energizer, but rather to minimize roughening of the surface of the steel which may be caused by the use of barium or sodium energizers alone.

These relations are represented in Fig. 1which represents the relative energizing abilities of the individual energizers as determined from carburizing tests made of mixtures of 90 parts of a low-ash carbon and l0l parts of carbonate of4 the energizer (see, Trans. Amer. Soc. Steel Treating, May 1925, p.- 635).` -This shows that of the alkaline earths barium oxide has the greatest energizing power, while lime alone is indeed a very poor energizer so that it vwould be expected that lime would be incapable of highly energizing carbon. v As appears from Fig. 2, the effectiveness of an energizer increases with increase in thel amount used until a maximum energizing effect is reached. But these curves show also that even with as much as 30 per centof lime, the carburizing activity of a mixture of carbon and lime is still below to, so that a carburizer made from carbon and lime alone would be commercially unsatisfactory. The carburizing activity of mixtures of carbon and alkaline energizers will vary with the type of carbon, the method of compounding. and the percentage of energizer.Y It is not possible, therefore,.to make a graph showing the absolute energizing poweiof these energizers for all carbons and proportions of carbon to energizer. However, with variations in the type and proportions of materials the general relationships expressed in Fig. l -would not be disturbed evenI though the actual energizing powers of the individual materials might vary somewhat from the values shown. Y f The activities of carburizing compounds ,may be comparatively related to one another by a simple test in which cleaned test pieces of a suit- 80, measured by the test referred 'l able steel and of convenientsize are weighed upon a chemical balance and then packed with carburizing compound in nickel-chromium alloy pots provided with tted covers which are luted in place. The containers are then heated in a furnace, such as a gas-fired semimuille furnace, to 1700 li'. After a suitable period of time, say ve hours, the containers are removed and cooled. The test pieces are then removed, cleaned if necessary, and again weighed. The gain in Weight is a measure of the activity of the compound. Extensive experience with this method of testing relative carburizing activities has shown that case depth and degree of surface carburization closely parallel the gain in weight, for which reason this method may be-taken as a standard for the purpose of obtaining relative carburizing eiiiciencies. A suitable test material isv coldrolled SAE 1020 steel cut into pieces 2% inches long, 1 inch wide, and 1% inch thick, such specimens weighing approximately 63 grams. The l pots used may suitably be about 'l inches deep and 2 inches inside diameter.

In applying such a test it is necessary to adopt some standard compound with which to make comparisons. The standard chosen in making the tests referred to herein was a com- Y mercially successful .compound in pelleted form and consisting of parts of carbon, 24 parts.

of barium carbonate, and 8 parts of lime, the three constituents being uniformly and intimate- Iy distributed through the mass of each pellet. The activity of this standard compound, measured by the gain in weight of a piece of SAE 1020 steel treated as just described, is arbitrarily given a test value of lill), and the activity of any other compound in th saine heat may'be figured as the relative gain in weight of its test piece. Thus, if a test piece treated with the standard compound gains 240 milligrams in weight, and a similar test piece in a second compound gains 200 milligrams in weight, the activity of the latter will be "200/240 of 100, or 83, which represents its relative carburizing activity.

It should be understood that the particular.

capable of absorbing carbon at-a rate faster than that represented by an activity of about to 120.

It has been proposed to add to ordinary lcarburizing compounds containing barium carbonate as the chief energizer, oxides of aluminum, nickel,

lead, copper, manganese, iron, and other metals.

Tests which I have made of such compositions show clearly that. the additions proposed are not materially benecial, and may be detrimental to the carburizers customarily used Ain the art and energized principally with barium carbonate, with sometimes sodium carbonate also, and that this is true Whether or not lime be additionally present.

V I have discovered, and it is upon this that my invention is predicated, that compositions consisting of carbon and lime may be activated to commercially acceptable activity by the addition of a heavy metal oxide, i. e., by such oxide these commercially inacceptable lime-carbon compositions become carburizers of satisfactory commercial activity and of at leastras great emciency as the carburizers activated by barium or sodium carbonates. or both, now in commercial use. Furthermore, this activating effect of heavy metal oxide on carbon-lime compositions is specic to lime alone. In .other words, the heavy metal oxide does not appear to super-activate energizers of the alkali and alkaline-earth groups other than lime.'

Stated in other words, I have found that heavy metal oxides are capable of increasing the energizing power oflime on carbon to an'extent such that a carburizer embodying characteristics rendering it entirely satisfactory from all commercial standpoints may be made from lime as the predominant or sole energinzer through the use of such heavy metal oxide, and also-that not only do the heavy metal oxides lack this beneficial effect upon the other energizers but may indeed decrease their energizing effect. Thus the essence of the invention resides in a carburizing compound in'which lime and heavy vmetal oxide constitute the principal and commercially effective aids to carburlzation.

The term heavy metal oxide as used herein vhas reference to the oxides of nickel, iron, and

chromium, and to a lesser extent manganese, gilmetals have atomic weights between 50 and 60.l

Because iron oxide is the commonest and cheapest of these oxides, and because for all practical purposes it is entirely satisfactory from the standpoint of its activating eect, reference will hereinafter be made to this member of this group by way of example, and not of limitation, in further illustration of theinvention.

The relationship just expressed may be understood readily from a consideration of Fig. 3. 'I'he various graphs of this gure represent the carburizing activity of compounds made from` carbon and 5 per cent of the particular carbonate indicated for each graph, plus iron oxide in the amounts which the abcissae of Fig. 3 represent. The composition made from carbon and lime alone showed -a carburizing activity of less than 50. Such a carburizer would be totally inadequate for commercial purposes, modern commercial requirements demanding a carburizer having anactivity of at least 80 as determined by the test referred to herein in all comparisons of such activity. But the addition of iron oxide to that carburizer in accordance with the invention progressively and substantially increased the activity so that at a content of slightly more than 1 per cent of iron oxide the compound reached commercially acceptable activity, and the activity was increased to substantially beyond the minimum commercially acceptable value by further additions of iron oxide.

of carbon and lithium carbonate, carbon and vsodium carbonate, carbon and barium carbonate,

and the others, some of which initially possessed high carburizing activity, were in each case detrimentally aiected by the addition of iron oxide, thus proving that the use of heavy metal oxide is speciiic to lime alone of the energizers ofthe alkali and alkaline-earth metals.

As noted hereinabove, this wasnot to be expected because previous knowledge in the art, as represented, for example, by Figs. 1 and 2, indicated no abnormal characteristic for lime, and it was not to be expected that lime alone of the compounds of high and andere? seven common energizers would be thus responsive to heavy metal'oxide.

I have found that relatively small amounts of lime and heavy metal oxide sumce to produce commercially acceptable activity, an advantage which reflects itself directly in low cost of the carburlzing compound. For example, as little as 3 parts of lime, calculated as calcium hydroxide, will produce a fairly l0 active compound-when mixed with 100 parts of -by ric. 2. t

'15 weak with consequent shortening in excess of about 10 per cent.

purposes the For most purposes I now pref-er to use froml i about 3 to 6 per cent of. lime with about 2 to about 5 or 6 percent of iron oxide, and for' most purposes. an entirely satisfactory compound. can be that these changes can madefrom 5 parts each of lime and iron oxide with 100 parts offcarbon. I t will be understood that the use of other heavy metal oxides may require some change in relative proportions but be'dtermined readily by means known to those familiar with the art.

As is customary in the art, the carbon used in making the compounds may be derived from a variety of sources. I

that where coal is used as the source of carbon,

' it should be mixed-with the lime and iron oxide prior to cokiiig, at least where particularly high carburizing -activity is desired. If coking coal is used, no other binder may be necessary, but since 40 a major aspect of the invention resides in bonded f that bonding may will appear, it will be understood be achieved in other ways known to the art, such as by the use oi molasses, for example.

Compounds, aS

The invention may be described furtherA with 65 bon and 5 parts of beyond that .75 lsix-ed carburizi'ng' activity.

reference to exemplary compositions.

Example 1.-100 parts by weight of powdered carbon, such as charcoal dust or pitch coke dust, are mixed with 5 parts of hydrated lime and 5 parts of finely powdered iron oxide. The mixture is then molded into pellets about 3A; inch in diameter, using molasses as a binding agent. The

pellets may bedried or heated to char the` mo-` lasses binder,

lt'smntplev 2.-As another example, 100 parts by weight of powdered low-ash coal are mixed with 5 parts of hydrated lime and 5 parts of iron oxide, and the mixture is then coked in containers out of ,contact with air. The resultant compound coke is crushed and screened to provide fragments of desired size, say those passing a 2-mesh and retained by a 4-mesh screen.

In the foregoing examples the base of the compound is a mixture cons ting of 100 parts of car- 1ime. Such mixtures are scarcely more activeA than carbon' alone in car- 'burizing steel, and 4they have no possible commercial value. The surprising feature of the invention is.' therefore, that the use of iron oxide increases the activitypf suchl a composition' to or of theusual commercial carburizing compounds containing large quantities of mixed and powerful energizers, and in which barium carbonate is chiefiyrelle'd on to produce the dehave discovered, however, e

. ing from conjoint use more than merely additive.

lAs further illustrative' of the invention, reference will now be made to tests of various coxn-v pounds which illustratev the principle 'on which the invention is were made according to the procedure of Example 2,)and the compounds were-tested in the manner just described. The following tabulation represents the constituents used in making the individual compounds and the average activity of each composition as determined from several successive heats. AltlioA h reference is made to coal in the tabulation it will be understood that this is to give the initial composition of the' mixture, l and that all of the mixtures were coked to prepare the In considering the foregoing data it should bel borne in mind that an activity of 100 represents approximately the average activity ofthe usual commercial carburizing compound, that an activity of 80 represents the lower limit which is com'- mercially acceptable, and that an activity of 1120 represents approximately the upper. limit of useful activityas controlled by the ability of the steel to' itself absorb carbon.

f Compound A shows that carbon alone is a wholly ineffective carburizing material, and Compound B that iron oxide is virtually without effect in energizing coal. Compounds C and D show that lime alone, even in an amount of 20 per cent, does not alone render carbon active enough to be commercially acceptable. Compound E, however, shows that a composition made up in accordance with this invention possesses an activity vastly superior to that of carbon alone, carbon and iron oxide, or carbon and lime. Compound E is also superior to those made from barium carbonate (F, G), and Compound oxide represses the powerful energizing eilect'of barium carbonate.

Comparison of Compound E vwith Compounds B and C' shows further that the activity flowof lime and iron oxide is Thus, iron oxide alone (Compound B) increases the activity of coal alone (Compound A) but 2 points, and lime alone (Compound C) increases it only l2 points. Hence the use of 5 parts each' of iron oxide and lime would increase (coalalone) 14 points if their joint use were render' the compound Iinitially of low andjunsatispredicated. These compounds the activity of Compound A H shows how heavy metal and among these the oxides of silicon factory activity. I have found that inthe practice offthe invention the iron oxide should be, accordi-ngly, of rather high purity. For instance, iron oxides of high silica content show virtually no activating effect when used in the practice of the invention. On the otherhand, iron oxidescontaining 98 per cent to 99 per cent of iron oxide are fully satisfactory. The same observa` tions apply also to the'other heavy metal oxides contemplated by the invention, i. e., they should be low-in or free from impurities which would tend to repress the activating influence of the heavy metal oxide, and of these silicates,partic ularly aluminum tionable. l.

'I'he purer iron oxides of commerce, such as those produced by precipitation from solution, by calcination of iron sulfate, and by oxidation of iron in contact with water, are sufficiently active for the purposes of this invention. I have found that the scale which is dislodged in the working,

e. g., forging and rolling, of'steel ingots, billets and the like, commonly known as mill scale,. affords a cheap source of iron oxide which is eminently satisfactory for the purposes of the present invention. 'I'his mill scale is friable and may be easily powderedwith no tendency to pack or agglomerate during pulverization. When finely powdered it is a very heavy black material which is as eective for the purposes of the invention Vas the bulkier and more expensive iron oxides produced byv precipitation or calcination methods to which ref erence has just been made. Also, the density of mill scale is advantageous because the dense powdered mill scale shows a lessened tendency to make soft coke or briquettes upon the heating of a mixture of itJwith lime and coal or other types of carbon. Y.

In general, the ingredients, especially the heavy metal oxide, should be in finely powdered form, the coarser oxides being of slight benefit. Furthermore, the nely powdered oxide, lime and carbon' should be intimately and uniformly mixed. Heavy metal oxide in the form of coarseparticles, or

unmixed with the carbon and lime, for instance when applied as a separate layer to the surface of the compound," does not afford the substantial 4clients may be mixed in a ball mill. may be coked, or it may beformed into pellets benefits of this invention.

To this end the mill scale, or other heavy metal oxide, should be finely powdered. For instance, it may be ground so that 98 per cent or 99 per cent of the material will pass a-'200-mesh standard screen. Y jl To insure intimacy of their mixing the ingrewhich are thenicoked. It wil intimate, bonded mixture of evident that an powdered ingredients may be produced upon the's'urface of supporting pellets or fragments, whether this base support be active or inactive. Most suitably, however, the materials are reduced to finely powdered form, mixed and then bonded by any suitable procedure.

A feature of eminent importance in achieving.

the highest activity in the practice of the inventionlis that the compositions should be subjected to a bonding treatment, in the course of production of the compound. Bonding is desirable, of

course, to maintain' intimacy, uniformityy and positive contact, and to avoid separation and segregation of the ingredients of the composition in handling and using it. I have found, however, that even where segregation is avoided without bonding it is still advantageous to bond the ingresilicates, are especially objec- The mixture diente firmly together if the fun advantage vef the invention is to be attained. Moreover, this feature appears to be of greaterimportance in the to the following tests.

Example .3.-100 parts by weight of powdered -loW-ash coking coal were mixed intimately with 5 parts of powdered hydrated lime and 5 parts of finely powdered mill scale. The mixture was coked and then crushed to a flne powder.

Example 4.-Some of the coal used in Example 3 was coked, crushed .to a fine powder, and 100 parts of this powdered Acoke then mixed with 8 parts of nely powdered mill scale and 8 parts ,of lime. The reason for increasing the amount of lime and mill' scale in this composition was that4r the particular coal used contained about 37 per cent of matter volatile in coking at 1700 F.

vAllowance was made therefore for the evolution of that volatile matter in the coking of the coal used in this examplel so that thecompositions of Ex-l Y amples 3 and 4 finally consisted of the same proportions of identical constituents, each in a ne state of sub-division, the difference being that in the process of manufacture one (Example 3) had been bonded and the other (Example 4)' had not.

Carburizing tests upon these compositions showed an activity of 117 for the bonded mixture of Example 3, and of 75 for the mixture of Example 4 which had not been bonded. After using the compositions for several heats, the unbonded lmixture of Example 4 was made into pellets, using molasses as a binding agent, and it then showed an activity of 120, as contrasted with 75 in the unbonded condition, thus bringing it to the activ-r ity of Example 3 and further evidencing the value of bonding. w

Example 5.-In another series of tests 100 parts by weight of finely powdered pitch coke containing approximately 1/2 per cent of ash and 9 per cent of volatile matter Was mixed with 4 parts of powdered iron oxide and 8 parts of hydrated lime. Part ofithis mixture (Ex. 5-A) was retained in the dry mixed condition, and part was mixed with about 20 per cent of tar to make a satisfactory bond when the mixture was briquetted and coked, This cokedA mixture was then crushed to a ne powder (Ex. 5-B) Carburizing tests showed an activity of 115 for the material (Ex. 5-13) that had been bonded and then powdered, and 80 for hereinabove, the carburizers provided by the invention are peculiarly sensitive to the poisoning effects of silicon oxides and other oxides and oxidic materials such as alumina and silicates,

especially aluminum silicate, which is the chief ingredient of coal ash.4 I have found, however, that by the use of coking coal containing less than 4 per cent of ash, and most suitably less than 2 per cent of ash, the benefits of the invention are fully-realized. ,Thus, excellent and inexpensivev carburizing compound can be'made by mixing 100 means, it would be a,

partsof finely powdered coking coal containing carburizers are avoided through the'practice of less than 4 per centv of ash with small amounts of this invention.

lime and heavy metal oxide, say 5 parts each of When a carburizlng pot containing the usual lime and mill scale, coking the mixture and crushbarium carbonate product is opened, especially if 5 ing the compound coke to secure fragments of it be opened while still hot, the' dust created is desired sizes. found to be particularly offensive to the sense of As indicative of the influence of coal ash upon v smell and irritating to the respiratory tract. In the carburlzers provided by this invention, com'- w contrast, the dust and odor (if any) from pounds made by coking briquetted pellets about compound made from carbon', lime and iron oxide l inch in size made from a mixture of floated f 'in accordance with this invention'is not offensive .l0

Eastern Kentucky coal containing 1.2 per cent of or irritating. Also, barium carbonate energizedash, with parts each of lime andl mill `scale compound may be objectionable because barium showed an initial activity of about 120 which was compounds are known to be poisonous, which is sustained unusually wellinre-use. Compounds not true of lime. Y

l5 made in the same manner and using the same It is well known'that carburizing compounds 15 proportions, but made. from Eastern Kentucky containing sodium carbonate,or sodium and barcoal with 5 per cent of ash, Pittsburgh seam\coal ium carbonates, attack alloy carburizmg pots, in with rl per cent of ash, and Cambria County some instances quite rapidly, causing corrosion (Pennsylvania) coal with 4.5 per cent of white and the formation of the so-called cancers,"

'20 ash, showed but about 80 per cent activity, and 4which materially shorten their useful life. While 20 the activity lessened rapidly with re-use. barium carbonate alone does not attack the pots While the preferred embodiment of the inve'nso rapidly, it is not certain that considerable, if g tion, contemplates compo ds vconsisting of carslow,Y attack and injury'do not, nevertheless, ocbon, lime and heavy metal oxide, it will be apprecur. In extensive and prolonged observation and4 ciated that other substances may be added for test upon the compounds provided by this inveng5 special purposes, including amounts' of -other ention I have not detected any'observable sign of erglzers, as long as the activity characteristic of attack upon the alloy containers in which it was the invention is not adversely affected. However, packed.` It appears. therefore,- based partly upon the simple cgmpositions stated give fully satisthis observation and partly upon the unusually 80 factory carburizlng activity, even to that which clean surface of the steel packed in my new com- 80 supplies carbon at the maximum rate at which pound, that its use will lengthen the usual life of it can be absorbed by steel, and therefore they are' 'these alloy carburizlng pots, thus further increasmost desirablel for most purposes. ing carburizlngeconomies.

From what has been said many of the advan- In summary, ear er investigators have, aspre- 'tagesl of the carburizing compounds made by ."viously stated,. sought to provide carburizers of 35 adding iron oxide or other heavy metal oxide to a increased activity by adding metal oxides to' carmixture of carbon and a small amount 'of lime asburizing mixtures initially having a commercially,

`the dominant and commercially effective or only acceptable activity attained by the use'of large energizer will be understood by those skilled in -Aamounts of energizers, chiey barium. The addi- 4o theart. These compounds arecharacterized by tion of metal oxidesto these highly active mix 4nhigh activity at all the usual carburizing tempertures can evidentlyimprove ythem little, if at all. atures, and they exhibit unusually well-sustained because of the inability of the steel itself to absorb I v activity when thecompound is subjected to recarbon faster than supplied by such acompound peated heats. For instance, compounds'made as energized principally by barium carbonate and described herein have been maintained attheir not containing the ancillary metal oxide. Fur- 5' original high activity by adding to the used comthermore, asshown by Fig. 3, any activation of pound after each heat-only 5 to 1 0 per cent .of calcium energizer present in the mixture would fresh compound, whereas it is customary and be offset by the adverse effect of the metal oxide necessary to add 10 to 35 per cent of fresh comon' the barium and'other -energizers, and this 5o pound of the older commercial types. probably explains why these prior proposals have `60 A major advantage -is the low cost due to the been without beneficial result. Tests upon these4 use of small' amounts of inexpensive calcium particular mixtures. have fully conrmed these hydrate and iron oxide instead of. rather 'arge statements. amounts of the more expensive barium carbo ate. It shouldbe .understood that the belief is that;

'a 55 The actual Sving'may amount to nearly' 10 per the so-called energizers, such as barium carbon- 55 ',cent of the selling price of the usual compounds ate andv calcium hydroxide, are not "effective as energized chiefiywith barlurncarbonate.-

. energizers until they have 'been reduced lto the 0f 88980181 interest SelQf Clblliizlngy corresponding, oxides, the reduction occurring compound is the fact tht OmDOunds according ,'-orinarily when the compound is raised to carc`0 -tothis invention produce unusually smooth-and vburning temperatures. Likewise. I now believe w @WNY mburized' illlfw.l The comliimdk that iron oxide and the like, which serve f heretofore used commercially containing to increascthe energizing elect of calcmm oxide 'carbonateorsodium carbonate, or both, frequent?! in `accordance with this invention, are not efly produces rough spots 'fand small 'semi-soluble fectlve until they-have been reduced to nely c5 adhesions upon the steel surfaces, and the areas ldivided. metal, asfiron or nickel, this reduction,

under these adhesions may be. msuillciently car"`=also, occurring when the., compound is heated burizedto harden successfully. sivingrise torso ft u to carburizing temperatures. For this reason it /,V spo f on the steel and the necessity 'of either is .possible l'to substitutel nely ydivided metals of carburlzlngror discarding the parts so fthis sort for the heavymetal oxides or other.-

The surface of steel carburized with the ,com-

reducible compounds, although probably' that im" pounds inaccordance with thisl invention has a wouldvnot be economical since the oxide -aflords smooth gray'appearance with no sign of rough- 'ja cheaper source or the metal. Inthis connecnem or adhesions and is evenly carburized overl tion it is to-observethat the molecuthe entire to the compound, i. e., the o! the calciumoxide and the atomic '76 rough spotsenco teredinthe use of the prior weight of those metals which increase-its er- 15 fectiveness, as well as the atomic weight of the v `material and energizer, etc. Most carbonaceous materials evolve gases and lose weight in being heated, and this loss of weight may be large; for

instance, the usual commercial charcoal will lose 25 per cent to 30 percent of its weight in being heated to carburizing temperatures; bituminous coal may lose 15 per cent to 40 per cent; sawdust,

tan bark and the like may lose as much as 85 per cent. Likewise, weight changes are involved in converting energizing carbonate to oxide, and heavy metal oxide to metal. For these-:reasons some claims are based upon the composition of the compounds at operating temperature, say about 1700 F.,since this gives a comparable relation of 4the constituents in actual use.

According to the provisions of the patent statutes, I Ahave explained the principle and manner of practicing my invention^and have illustrated and described what I now consider to represent' its best embodiment. However, I desire to have it understood that, within the scope of the appended lclaims, the invention may be practiced otherwise than as speciiically 'illustrated and described.

I claim:

1. A carburizing compound comprising carbonaceous material, lime as the principal effective added energizer, and an activity-promoting material selected from the group consisting of finely divided metal having anatomic weight between 50 and 60 and finely divided reducible compound of such metal, said activity-promoting material being present man amountsuilicient to render thec'ompound of commercially acceptable carburizing activity.

2. A carburizingcompound comprising 'a bondedmixture of Acarbonaceous material, lime as the principa1eiective added energizer, and an activityepromoting material selected fromthe groupconsistin'g of iinely divided iron and iron oxidefin'an amount sufficient to render the comp ound of commercially acceptable carburizing activity.

3. A carburizing compound comprising a bonded mixture of Vcarbonaceous material, at least. about 3 per cent of lime as the principal effective added energizer, and at least about-2 per centof nely divided oxide of a metal having an atomic weight between 50 and 60 which cooperates with said lime to render the compound of commercially acceptable carburizilng activity.

4. A carburizing compound comprising a bonded mixture of carbonaceous material, at least about 3 per cent of lime as the sole added energizer, and at leasil about 2 per cent of iron oxide, said lime and iron oxide cooperating to render the compound of commercially acceptable carburizing activity. Y

5. A carburizing compound comprising a bonded mixture of carbonaceous material, about 5 per cent of lime as the sole added energizer, and about 5 per cent of finely divided iron oxide, said lime and iron oxide cooperating to render the compound of commercially acceptable carburizing activity. l

6. A carburizing compound comprising a bonded mixture of carbonaceous material, lime as the principal effective added energizer, and an amount of nely divided metal having an atomic weight between 50 and 60 suicient to render the compound of commercially acceptable carburizing activity.v I

HUGH RODMAN. 

